In the case of an acoustic piano, when a key of a keyboard is pressed, the damper felt gets away from the string according to rotation of a damper lever, an action comes into operation responding pressing of the key, a hammer strikes a string, vibration of the string is transferred to a sound board, and a music sound is emitted. It is configured that the damper felt is in contact with the string and suppresses vibration at the normal time (when the key is not pressed).
In the case of an electronic piano, it is conducted to improve reality of the sound by providing various additional sound and additional effects other than the actual sound of the piano which becomes main, and to make the sound similar to the emitted sound of an acoustic piano.
For example, in an acoustic piano, when plural keys are pressed simultaneously to emit the sound of a chord and the like, respective strings are struck by hammers corresponding to respective keys, the damper felts come to a state of getting away from respective strings, and therefore resonance (string resonance) occurs between plural strings.
In order to reproduce such string resonance, in an electronic piano of a related art, a process of providing an effect of resonance to a sound source at the on-position of the key that emitted a music sound was conducted.
Also, in Japanese Patent No. 2933186, there is disclosed an electronic musical instrument that controls the echo characteristic of the echo sound according to the key pressing information of each key configuring a keyboard, and it is described to conduct a process for providing an effect caused by an echo sound to a sound source.